The present invention relates to amplifiers and, more particularly, to switchable power amplifiers having a high level of efficiency over a broad range of output power levels.
Amplifiers such as transistors are commonly used to increase the strength of electrical signals. To increase the strength of an electrical signal, typically, the electrical signal is used to control a flow of energy from an energy source, e.g., a battery, through the amplifier to produce an output signal that varies in the same way as the electrical signal but has a larger amplitude. Generally, it is desirable to efficiently amplify the electrical signal using a minimal amount of power to reduce energy costs and increase battery life, for example.
The efficiency of an amplifier varies with operating conditions. For example, an amplifier designed for power efficiency at one output power level may be less efficient at another output power level. Many devices, such as wireless communication devices, require the amplifier to operate over a variety of output power levels. Typically, an amplifier is adjusted to achieve a peak efficiency at a single output power level, e.g., the maximum output power level. If the amplifier is designed for efficiency at the maximum output power level, the amplifier tends to operate less efficiently at lower output power levels. Accordingly, more energy will be consumed at lower output power levels than if the amplifier were designed for efficiency at the lower output power levels.
One technique for addressing efficient power amplification at more than one output power level is disclosed in U.S. Pat. No. 6,181,208 to King et. al., entitled Switchable Path Power Amplifier With Schotky Diode Combining Circuit, incorporated fully herein by reference. In U.S. Pat. No. 6,181,208, two separate power devices are employed. One power device is designed for efficiency at a first output power level and is used exclusively to deliver power for a first power output range and the other power device is designed for efficiency at a second output power level and is used exclusively to deliver power for a second power output range. The use of two power devices designed for efficiency at two different power levels in a mutually exclusive arrangement allows for increased efficiency across a broader range of power levels. However, using mutually exclusive power devices to achieve efficiencies at two different output power levels results in inefficiencies in terms of system components, since, at any given time, only one power device is being used.
Therefore, there is a need for an amplifier that efficiently delivers power at more than one output power level while efficiently utilizing system components. The present invention fulfills this need among others.
The present invention provides for an amplifier apparatus and method for efficiently amplifying electrical signals at two or more output power levels. The amplifier apparatus and method overcome the aforementioned problems by using a first stage amplifier that can be configured in at least two power states, a second stage amplifier that can be configured in at least two power states, and a state determination circuit for configuring the first and second stage amplifiers based on output power. To efficiently deliver power at one output power level, the circuit selectively configures the first and second stage amplifiers to each operate in one of their output power states. To efficiently deliver power at another output power level, the circuit selectively configures the first and second stage amplifiers to each operate at another of their output power states.
One aspect of the present invention is an amplifier including a first stage amplifier having at least two power states, the first stage amplifier having an input for receiving a signal, a control port, and an output; a second stage amplifier having at least two power states, the second stage amplifier having an input coupled to the output of the first stage amplifier, a control port, and an output; and a state determination circuit coupled to the control port of the first stage amplifier for selectively configuring the first stage amplifier in one of the at least two power states and further coupled to the control port of the second stage amplifier for selectively configuring the second stage amplifier in one of the at least two power states.
Another aspect of the invention is a method for amplifying a signal passing from a source to a load. The method includes determining an output power level of an amplifier, configuring a first stage amplifier of the amplifier in one of at least two states based on the determined power level to amplify the signal, and configuring a second stage amplifier of the amplifier in one of at least two states based on the determined power level to amplify the signal as amplified by the first stage amplifier.